Chronic exposure to stress has been implicated in a variety of physical (e.g., cardiovascular, gastrointestinal, respiratory) and psychological (e.g., anxiety, depression) conditions, resulting in substantial human, medical and financial toll. Stress is not a unitary phenomenon, however, and although there are some common biological and behavioral response patterns in most species, each organism responds to stress in a unique manner that reflects its particular experience, life history and genetic code. Thus, much basic and applied science has focused on understanding the internal and external forces that modulate the response to stress, which in turn helps inform us about the etiology of a variety of stress-induced physical and mental disorders. The influence of early environmental events in shaping an organism's biology and behavior has been explored using a variety of paradigms and species, including pre- and post-natal manipulations in rodents (largely due to their relatively short pre- and post-natal timeframes). Studies using prenatal stressors, postnatal handling, maternal separation and cross-fostering all illustrate the biobehavioral sensitivity of the developing organism. These studies leave little doubt about the potent effect that environmental experience can exert on an organism's developmental trajectory. However, these approaches may tell only part of the story. An organism's genotype is often expressed in the context of a dynamic interplay with external circumstances, in essence allowing environmental programming to shape the expression underlying genetic tendencies. The current proposal therefore seeks to extend these findings by using maternal separation and cross-fostering in a model of heightened reactivity to determine the effects of early experience on behavioral, cardiovascular, and neural response systems. Completion of the project will require behavioral observations, cardiovascular profiling, pharmacologic assessment, and central neural studies in order to direct multiple levels of analyses on the experimental questions. These data have the potential to provide information regarding the regulation of normal biobehavioral processes as well as suggesting etiologic mechanisms which may be involved in certain physical and mental disorders. Consistent with the mission of the AREA program, this project will provide a significant training and educational opportunity for undergraduate students.